MOTION MOUNTAIN

192 4 images and the eye – optics
Challenge 184 ny
Ref. 146
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The simplest imaging system are eye glasses. A child that has no proper glasses misses
an important experience: seeing the stars. Such a child will not understand the famous
statement by Immanuel Kant: ‘Two things fill the mind with ever new and increasing
admiration and awe, the more often and persistently thought considers them: the starred
sky above me and the moral law inside me.’ Always be sure that children can see the stars.
Two lenses of 40 cents each are sufficient to change the life of a child or that of an
adult. See the website www.onedollarglasses.org for an effective way to do it across the
world.
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How does the eye correct pixel (photoreceptor) failure? How many pixels are bad in a
typical eye?
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Infrared light can be seen, if it is of sufficient intensity. (Never try this yourself!) People
who observed such light sources – semiconductor lasers, for example – saw it as a white
spot with some red borders. In other cases, it is also possible to see short infrared pulses
through double-photon absorption in the retina; in this way, infrared of1000 nm producesagreenflashinsidetheeye.
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Among vertebrates, the largest eye is the eye of the blue whale; it has a diameter of55 mm.
(Only squids have larger eyes.) The smallest vertebrate eye seems to be that of juvenile
Brookesia micra, a small chameleon whose head is half the size of the head of a match
and whose eye is around0.3 mm in diameter.
The eye is a wonderful organ. To learn more about it, read the beautiful book Simon
Ings,The Eye–ANatural History, Bloomsbury,2007.
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In many applications, it is important to avoid reflections. Anti-reflection coatings are
used on the glass of shop-windows,and in lens systems that need to work in dim conditions,whenlightisscarce.Alsoliving
beings have anti-reflectioncoatings;theeyesof
moths are famous for appearing black also in bright daylight, because they do not reflect
light. Various companies are trying to reproduce this so-called moth-eye effect in
commercialapplications.
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Moderntechnologyallowsproducingmicroscopesatlowcost.Forafascinatingexample,
seethe1Euromicroscopethatcanbefoldedfromasheetofpaper,embeddedwithsome
additionaldevices, and is shown in Figure 142.The device is used by holding it in front of
the eye or by holding it in front of a lamp and observing the projected image on a screen.
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If a sufficient number of images is available, it is possible to identify the camera that produced
them. Every camera has a specific image noise pattern; by extracting it through
Motion Mountain – The Adventure of Physics copyright © Christoph Schiller June 1990–November 2015 free pdf file available at www.motionmountain.net